In a modern digital communications system, a source device generates a digital signal that indicates analog signal amplitude, and sends the digital signal to a target device in a form of data by using a transmission system. The target device converts the digital signal into an analog signal, or uses the digital signal to perform digital signal processing. A most typical application is an IQ signal in a common public radio interface (Common Public Radio Interface, CPRI) specification. In a downlink direction, as a source device, a radio equipment controller (Radio Equipment Controller, REC) transmits an IQ signal to radio equipment (Radio Equipment, RE), and the RE converts the digital signal into an analog signal. In an uplink direction, as a source device, the RE converts an analog signal into a digital signal (an IQ signal) and transmits the digital signal to the REC, and the REC performs uplink digital signal processing.
However, when data is lost in transmission, the source device retransmits the data. Retransmission in the prior art increases a delay, and is inapplicable to a low-delay transmission system. For example, the CPRI specification has a high requirement of a delay, and a delay caused by retransmitting lost data is unacceptable.